The present invention relates to technology for preparing a silicone compound (a polysiloxane) and, more particularly, to a novel method for the polymerization of a linear silalkylenesiloxane by subjecting the corresponding cyclic silalkylenesiloxane to ring opening polymerization.
Silicone compounds (polysiloxanes) have excellent thermal resistance, high anti-weathering properties, and unique electrical properties, etc., so that they are used in diverse fields. Various attempts have also been made to attain improvements in their performance capabilities and properties. Polysilalkylenesiloxanes are one such group of silicone compounds having improved properties. Polysilalkylenesiloxanes are now drawing attention as polymers which, as compared with the dimethypolysiloxanes extensively utilized in various fields, have excellent resistance to acid, alkali and so on, and also remarkable mechanical strength, as they are produced by introducing silalkylene bonds such as silethylene bonds into the main siloxane chain moiety.
As a process for the preparation of polysilalkylehesiloxanes, there has been reported a process in which a cyclic silalkylenesiloxane is subjected to ring opening polymerization by means of anionic polymerization using lithium silanolate as an initiator under alkaline reaction conditions (B. Suryanarayanan et al., J. Polym. Sci., 12, 10891109 (1974)). Modified forms of the process include, e.g., a process for subjecting a cyclic silalkylenesiloxane to ring opening polymerization by using potassium silanolate as an initiator and divinylsiloxane as a chain transfer agent (Examined Japanese Patent Application Publication No. 15614/1994: Japanese Patent Application No. 178727/1990) and a process for the ring opening polymerization by using water as a chain transfer agent (Examined Japanese Patent Application Publication No. 62773/1994: Japanese Patent Application No. 178727/1990). The reaction operations of such prior art technologies are, however, laborious because they require the use of a chain transfer agent for regulating the molecular weight of the resulting product due to the fact that they are based on the living polymerization by the anionic polymerization under alkaline conditions.
The present inventors have found a novel method that can produce a linear polysiloxane from a cyclic siloxane compound by means of ring opening polymerization that is carried out using the silane compound and a particular transition metal catalyst under neutral conditions yet that does not require the use of any chain transfer agent.
Therefore, the present invention provides a method for the preparation of a linear polysilalkylenesiloxane having a repeating unit represented by the following general formula (4): 
(where b is an integer of 1 to 4; and R is a hydrocarbon group of from 1 to 8 carbon atoms),
which comprises subjecting a cylic silalkylenesiloxane represented by the following general formula (3): 
(where b and R have each the same meaning as above)
to ring opening polymerization by using as a catalyst a polynuclear ruthenium-carbonyl complex with carbonyl groups coordinated with three or four ruthenium atoms, in the presence of a silane compound represented by the following general formula (1): 
(where X1, X2 and X3 are the same or different, each being a functional group or atom selected from a group consisting of hydrogen atom, a halogen atom, an amino group, an alkyl group, an alkoxy group, a thioalkyl group, an alkylamino group, an aryl group, an arylamino group, a vinyl group, a siloxy group, an organo-siloxy group, an organo-silyl group and a heterocyclic group)
or by the following general formula (2): 
(where X1, X5, X6 and X7 are the same or different, each being a functional group or atom selected from a group consisting of hydrogen atom, a halogen atom, an amino group, an alkyl group, an alkoxy group, a thioalkyl group, an alkylamino group, an aryl group, an arylamino group, a vinyl group, a siloxy group, an organo-siloxy group, an organo-silyl group and a heterocyclic group; and a is an integer of 1 to 4).